Gas turbine electric power plants are utilized in so-called base load, mid-range load and peak load power system applications Combined cycle plants are normally used for the base or mid-range applications while the power plant which utilizes a single gas turbine as the generator drive is highly useful for peak load applications because of its relatively low cost.
In the operation of gas turbines, particularly in electric power plants, various kinds of control systems have been employed from relay-pneumatic type systems, to analog type electronic controls, to digital controls, and more recently to computer based software controls. U.S. Pat. No. 4,308,463--Giras et al., assigned to the assignee of the present invention and incorporated herein by reference, lists several of such prior systems. That patent also discloses a digital computer based control system for use with gas turbine electric power plants. It can be said that the control system described in U.S. Pat. No. 4,308,463 is a predecessor to the system described in the present invention. It will be noted that the Giras et al. patent is one of a family of patents all of which are cross referenced therein.
Subsequent to the Giras et al. patent, other control systems have been introduced by Westinghouse Electric Corporation of Pittsburgh, Pa. under the designations POWERLOGIC and POWERLOGIC II. Similar to the Giras et al. patent these control systems are used to control gas tubrine electric power plants. However, such control systems are primarily micro-processor based computer systems, i.e. the control systems are implemented in software, whereas prior control systems were implemented in electrical and electronic hardware.
The operating phiolosophy behind the POWERLOGIC and POWERLOGIC II control system is that it shall be possible for the operator to bring the turbine generator from a so-called ready-start condition to full power by depressing a single button. All modes of turbine-generator operation are to be controlled including control of fuel flow furing large step changes in required power output.
The present invention constitutes an improvement to the POWERLOGIC II system. Ignition in prior combustion turbines, for example the W501D5, utilize compressor discharge pressure as a measure for determining when ignition should occur. Unfortunately, this so-called constant pressure ignition is effected by ambient conditions such as air temperature and the temperature of the metal parts of the turbine itself. It can be shown that ambient temperature can effect air flow through a combustion turbine by as much as 6 percent. The possibility exists that certain fuel/air conditions which are outside the ignition envelope of the combustion turbine could occur. Consequently, a need exists for more reliably determining when optimum conditions re present for the ignition process.
Although, the operation of a gas turbine electric power plant and the POWERLOGIC II control system are described generally herein, it should be noted that the invention is particularly concerned with enabling the ignition process in gas turbines.